The present invention relates to a supply voltage detection circuit for detecting supply voltage levels.
Recently, many of the processors, such as microcomputers designed for portable equipment, are equipped with a supply voltage detection circuit supply voltage detection circuits find application in detecting the life of a battery, the voltage of a capacitor power source used in a backup mode and so on. In addition to these detection applications, supply voltage detection circuits have been used extensively for generating signals such as a reset signal for initializing the system when the power is turned on and a reset signal for preventing the system from getting out of control when there occur variations in power supply.
A typical supply voltage detection circuit is comprised of a monitor circuit for supplying a detection voltage Vdet reflecting a supply voltage Vdd, a reference voltage generation circuit for generating a given reference voltage Vref not depending upon the supply voltage Vdd, and a comparator for comparing the detection voltage Vdet with the reference voltage Vref and outputting the result of the comparison. For example, the monitor circuit is formed by a resistive potential division circuit which produces the detection voltage Vdet proportional to the supply voltage Vdd. BGR (Band-Gap Reference) circuits have been known in the art as one type of the reference voltage generation circuit. With the BGR circuit, the reference voltage Vref can be obtained with high precision, as shown by Banba et al. in their report entitled xe2x80x9cA CMOS Band-Gap Reference Circuit with Sub 1V Operationxe2x80x9d, 1998 Symposium on VLSI Circuits, Digest of Technical Papers, pp. 228-229. On the other hand, a reference voltage generation circuit of lower precision than the BGR circuit has also been known in the art. Such a low-precision circuit is shown in U.S. Pat. No. 5,969,549 to Kim et al.
However, in the above prior art technique, the monitor circuit, the reference voltage generation circuit, and the comparator are all in the operating state at all times. Therefore, the problem of large power dissipation arises. Particularly, when employing a BGR circuit as a reference voltage generation circuit, such a power dissipation problem becomes much serious.
Accordingly, an object of the present invention is to provide a supply voltage detection circuit capable of high detection precision/low power dissipation compatibility.
In order to achieve the above object, the present invention provides a supply voltage detection circuit which employs a configuration comprising a monitor circuit for supplying a detection voltage reflecting a supply voltage, a reference voltage generation circuit for generating a reference voltage, and a comparator for comparing the detection voltage with the reference voltage and outputting the result of the comparison, wherein a first voltage range including the reference voltage and a second voltage range different from the first voltage range are set, and wherein the supply voltage detection circuit further comprises control means for performing control so that the current dissipation of the reference voltage generation circuit is reduced when the detection voltage falls within the second voltage range in comparison with when the detection voltage falls within the first voltage range.